iOS 5.1, which is on the right, only shows four app rows when run in the same iOS simulator app. That's telling, since there would be little reason to add the support for an additional row if the screen was not going to get bigger. 9to5mac also reports that the simulator will not display the five rows at any resolution other than 640x1136, suggesting that Apple's not just trying to squish as many apps into the current screensize as it can. Other higher-than-current-iPhone resolutions scale iOS 6 to the iPad's home screen.